The surface plasmon erupted by bare metallic film has limitation of localizing high intensity field. Thus, nanostructures on the metallic film (such as nanowire, nanopost) have been used to enhance the Plasmon field by antenna effect. In the case of nanowire, field is highly localized at the sharpened edge of the nanowire. If there is an additional enhancing factor such as a gap between the edges of the nanostructures, area of highly localized field is formed. By adopting reversed trapezoidal structure, we expected to control area and intensity of highly localized plasmon field from both the nano-antenna effect and the gap plasmonic effect. So, we simulated trapezoidal nanowire structure changing the ratio of bottom length and top length of nanostructure. Then we can observe the variation of Plasmon field and intensity. In addition, we can obtain unusual result that the intensity of Plasmon field is highly reduced at specific ratio of bottom length and top length.
Surface enhanced Raman spectroscopy (SERS) based on plasmonic colocalization between DNA attached gold nanoparticles and silver nanoislands substrates. Raman spectra measured on a silver nanoislands substrate were observed 20 and 1.8 folds signal enhancements relative to them on a film substrate with high and low numerical apertures of lenses, respectively. By comparison between calculations and experiments results, we proved that distinct differences of the signal enhancements came from changing field of view on random nanoislands substrate. Consequently, we show that nanoislands substrates with a precise position control can be a good candidate for a SERS substrate which can achieve significant signal enhancements without a complicated lithographic process.
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